This invention relates to surface mount packages for semiconductor devices, and more specifically relates to a novel surface mount package in which the conductive metal plug to be connected to a surface heat sink is connected to the side of the semiconductor die containing the heat-generating junctions to improve cooling efficiency and to reduce the resistance of MOS-gated semiconductor devices.
Surface mount packages are in widespread use and normally consist of a semiconductor die mounted with its back surface in contact with the surface of a lead frame and with its front surface having wires from connection pads to the lead extensions of the lead frame. The bottom of the lead frame is then located atop a heat-conducting slug, the bottom surface of which is to be connected to a flat surface which subsequently receives the surface mount package. The assembly of die, lead frame and heat-conducting slug are then over-molded, with the flat bottom surface of the slug exposed for surface connection, and with the lead frame leads extending out of the molded housing to be available for external connection.
This standard surface mount package design has the disadvantage, particularly in the case of MOS-gate controlled devices, that heat is generated primarily at the top of the die, so that heat must flow through the full thickness of the silicon die, and through the metal slug at the die bottom to the heat exchange surface to which the device is mounted. This increases the temperature of the device at a given load condition and increases the on-resistance or forward voltage drop of MOS-gate controlled devices. In addition, the source or emitter bond wires add resistance and inductance to the device, and the current flow in the surface metallization adds to the resistance as well.